There are several types of treatments in which blood is extracted in an extracorporeal blood circuit. Such treatments involve, for example, haemodialysis, haemofiltration, haemodiafiltration, plasmapheresis, blood component separation, blood oxygenation, etc. Normally, blood is removed from a blood vessel at an access site and returned to the same blood vessel or at another location in the body.
In for example the cases of haemodialysis, haemofiltration, haemodiafiltration, and plasmapheres, but not limited to these cases, a treatment fluid (also referred to as a dialysis fluid) is made approximately isotonic with a patient's blood. The treatment fluid and the patient's blood are made to flow on each side of a semi-permeable membrane of a membrane device (referred to as a dialyzer). Diffusive transfer is achieved from one side of the membrane to the other when the concentration of the substance on each side of the membrane differs. Such substances may be impurities in the blood (urea, creatinine, etc.) which thereby migrates from the blood to the treatment fluid. Since fluid normally has to be removed from the patient during haemodialysis, a convective transfer by ultrafiltration, resulting from a pressure difference created between the blood side and the treatment fluid side of the membrane, is added to the diffusive transfer.
An apparatus for extracorporeal blood treatment includes a treatment control monitor (dialysis monitor) which is connected to a disposable extracorporeal blood circuit. The disposable extracorporeal blood circuit includes blood transport lines (in general an arterial line for blood removal from the patient, and a venous line for blood return to the patient) and the membrane device for blood treatment.
The semi-permeable membrane of the membrane device divides a blood compartment, connected to the blood transport lines, and a fluid compartment, connected to treatment fluid supply and discharge circuits. The blood transport lines are further coupled to a sensor and actuator system equipped on the treatment control monitor, which system normally comprises means for blood circulation, pressure sensors, air bubble sensor, one or more circuit blocking clamps, blood detector, etc.
The treatment fluid supply circuit receives purified water from a water supply system. The water system may be a small unit providing water to only a single treatment control monitor but may also be a large unit providing water by means of a water system loop arrangement to a significant number of treatment units in for example a hospital or a clinic.
Dialysis fluid, which may come into contact with the patients' blood, is often prepared from the purified water by means of a treatment fluid supply circuit. It is of paramount importance that the dialysis fluid used for the treatment is free from virus, fungi, bacteria and their residue and degradation products, such as endotoxins.
Therefore, the treatment fluid path of a dialysis monitor may be disinfected between dialysis treatments in order to reduce the presence of virus, fungi, bacteria, etc in the treatment fluid path. Chemical disinfection (e.g. using NaOCl or other chemical disinfection agents) is an efficient way to reduce the presence of bacteria, etc but it makes great demands on the following rinse procedure and requires very close measuring to assure that the treatment fluid path is free of chemical residual products before being used for subsequent treatments. The chemical process is not environmentally friendly and may have a negative effect on the life-length of the disinfected parts and components.
In an alternative disinfection process, thermal disinfection is achieved by letting hot water pass through the treatment fluid path. As a result, the problem of chemical residual products does not exist, the process puts less load on the environment, and has comparatively less negative effect on the life-length of the disinfected parts and components.
Thermal disinfection of a monitor is preferably carried out after the treatment of each patient. As the number of dialysis patients increases there is a need to increase the available time for treatments in the clinics. Consequently, there is a desire to reduce the time spent on disinfection between treatments.
Furthermore, before dialysis treatment can be commenced for a patient, the dialysis monitor needs a certain time to start up the production of treatment fluid with the correct composition and set temperature. Again, as the number of dialysis patients increases there is a need to increase the available time for treatments in the clinics. Consequently, there is a need to reduce the time spent on the starting-up of, or preparation of, the treatment fluid before the dialysis treatment can be commenced on the patient.